It is well known in variable displacement axial piston swashplate pumps and motors to control the position of the swashplate by porting fluid under pressure to one of two servos having pistons attached to the swashplate (the stroking servo) and by porting fluid in the other servo (the destroking servo) to drain. The control of such fluid is governed generally by a control valve having a control spool which has a feedback linkage connection to the swashplate. In such control valves, it has been desired to obtain what is commonly known as a wide band neutral to allow for a substantial degree of control spool movement prior to porting pressurized fluid to the stroking servo. By substantial it is meant that the control handle has to be moved three to four degrees from neutral before fluid is ported to the servo. When a wide band neutral control is used in a variable displacement pump of a hydrostatic transmission for a vehicle, it is possible that in certain unpredictable instances the vehicle could hesitate before coming to a stop when the control lever is rapidly returned to neutral. Sometimes this hesitation is sustained for as long as ten seconds. The hesitation generally exists when the swashplate is rapidly moved from maximum stroke to neutral.
The lands on the control spool in such control valves are generally equal to or wider than the servo ports in the valve. The reason for this is that if the lands are made narrower than the servo ports, interflow leakage can exist between the pressurized fluid and drain. Such interflow leakage can be at an unacceptably high level which will cause an excess of fluid flowing from the charge pump to drain through the control valve thereby reducing the amount of fluid that is available from the charge pump to the closed loop hydrostatic transmission system. It is to the preceding referenced hesitation that applicant's disclosure is directed.